EP3134905B1 - Data cable - Google Patents

Description

The invention relates to a data cable for high-speed data transmission with the preamble of claim 1.

Such a data cable is for example from the US 2012/0145429 A1 refer to.

In the field of data transmission, for example in computer networks, data cables are used for data transmission, in which typically several data lines are combined in a common cable sheath. In high-speed data transmissions, shielded wire pairs are used as data lines, the two wires in particular running parallel to one another or alternatively being twisted together. A respective wire consists of the actual conductor, for example a solid conductor wire or a stranded wire, which is surrounded by insulation. The pair of wires of a respective data line is surrounded by (pair) shielding. The data cables typically have a plurality of pairs of wires shielded in this way, which form a cable core and which are surrounded by a common outer shield and a common cable jacket. Such data cables are used for high-speed data connections and are designed for data rates of greater than 5 Gbit / s, in particular> 14 GHz. The outer shield is important for the EMC and the EMI properties, it does not transport any signals. In contrast, the respective pair screen determines the symmetry and the signal properties of a respective pair of wires.

Such data cables are typically so-called symmetrical data lines, in which the signal is transmitted via one wire and the inverted signal via the other wire. The differential signal component between these two signals is evaluated, so that external effects which affect both signals are eliminated.

Such data cables are often pre-assembled on plugs. In applications for high-speed transmission, the connectors are often designed as so-called small form pluggable connectors, or SFP connectors for short. There are different versions, for example so-called SFP-, SFP +, or CXP- QSFP connectors. These connectors have special connector housings, such as those from the WO 2011 072 869 A1 or the WO 2011 089 003 A1 can be seen. Alternatively, a direct so-called "back plane" connection without a plug is also possible.

Inside, such plug housings have a printed circuit board or circuit board, some with integrated electronics. The respective data cable must be connected to the rear of the connector on this board. The individual wires of the data cable are soldered or welded to the board. At the opposite end of the board, this typically forms a tongue with connection contacts, which is inserted into a mating connector. Such boards are also called paddle cards.

The pair shielding of a respective pair of wires is - such as from the EP 2 112 669 A2 can be seen - designed as a longitudinally folded foil shield. The shield is therefore folded in a longitudinal direction of the cable around the pair of wires, the two ends overlapping in a longitudinally overlapping area. The shielding film used for the shielding is a multi-layer shielding comprising at least one conductive (metal) layer and one insulating layer. An aluminum layer is usually used as the conductive layer and a PET film is used as the insulating layer. The PET film is as a backing is formed, on which a metallic coating is applied to form the conductive layer.

In addition to the longitudinally folded shielding in the case of pairs guided in parallel, there is basically also the possibility of helically wrapping such a shielding film around the pair of wires. However, at higher signal frequencies from around 15 GHz, such a spanning of the wire pair with a shielding film is not readily possible due to the design due to resonance effects. For these high frequencies, the screen foil is therefore attached as a longitudinally folded foil.

However, such a longitudinally applied film has an undesirable, negative side effect. The so-called common mode signal, also referred to as a common mode signal, is no longer sufficiently attenuated in the case of longitudinally folded shields, as is the case when wrapping with a shielding film.

The emergence of the common mode signal or common mode signal in such symmetrical lines with parallel pairs is known in principle. Attenuation of this undesired common mode signal is also made more difficult by the fact that this common mode signal component generally propagates faster than the differential signal component that is actually of interest. The loss or greatly reduced attenuation of this common mode signal compared to the wound wire pairs therefore leads to a deterioration of the so-called skew or the so-called mode conversion performance.

Such high-speed data connections generally aim to increase the transmission performance. The transmission rates and thus the frequency range of such data cables therefore increase more and more, and with it the problems associated with the common-mode signal components.

According to the US 2012/0145429 A1 To reduce resonance effects, it is proposed, among other things, to wind two shielding foils in opposite directions, with their electrically conductive sides facing one another.

From the US 2004/245009 A1 A data cable with a shield structure can be found, the shield structure having two conductive foils each wound on a gap.

In the JP 2014 017131 A describes a data cable with a shield structure which has two conductive foils which are wound in opposite directions to one another and each with an overlap.

Proceeding from this, the object of the invention is to enable improved data transmission with high signal frequencies of greater than 10 GHz in such a high-speed data connection.

The object is achieved according to the invention on a device with the features of claim 1. Preferred further developments are contained in the subclaims.

The data cable designed for high-speed data transmission comprises at least one and preferably a plurality of wire pairs made up of two wires extending in the longitudinal direction, each wire pair being surrounded by a foil-like pair shield. The pair shield has a first inner shield foil and a second outer shield foil, the inner shield foil being wrapped around the pair of wires. The two shield foils are electrically contacted.

This embodiment is based on the consideration of combining the advantages of a helical pair shield with those of a longitudinally folded pair shield. This embodiment is based on the knowledge that the resonance effects which occur in the case of a helically wound pair shield at high signal frequencies are based on the fact that, in the case of a conventional wound pair shield, which is usually multilayered, the two conductive layers are insulated from one another in the overlap region of the wound shield and thereby a capacitor is formed. At the same time, the helical winding results a coil, so that overall a resonant circuit is formed with a predetermined resonance frequency, which can no longer be shifted to higher frequencies by design measures in the conventional design.

The construction of the pair shielding by means of two layers which are electrically connected to one another reliably prevents the formation of such a resonant circuit, since there is no coil-like winding due to the electrical connection, and the coil is therefore virtually short-circuited. The resonance frequency is the root of (1 / (L ^∗ C)). Since the inductance is at least significantly reduced, the resonance frequency can easily be set to greater than 15 GHz. In contrast to this, this resonance or cut-off frequency is limited upwards to approximately 15 GHz in the case of conventional wound around with a metal foil, depending on the geometry. In this respect, the basic concept of a longitudinally folded pair shielding is at least adopted from the functional result. At the same time, the wrapping - preferably with an overlap - reliably suppresses the disadvantage of a longitudinally folded pair shield, namely the high common-mode signal. Overall, the pair shielding described here, with the structure of the two shielding foils, therefore achieves efficient shielding without disruptive side effects. Resonance effects with a correspondingly high attenuation of the signal and - in particular if the inner shield foil overlaps - insufficient attenuation of the common mode signal are effectively avoided. Compared to a longitudinally folded film, this structure is also characterized by simpler manufacture, better symmetry and increased (bending) flexibility.

The cores of a respective pair of cores in particular run parallel to one another and are therefore not twisted.

The inner shield foil is still wrapped around the pair of wires with an overlap. The desired attenuation of the common mode signal is advantageously reliably achieved by the overlap.

The width of the screen films is typically in the range from 4 to 6 millimeters.

A comparatively large overlap is set in the range from 20% to 40% of the width. With this configuration, a lower cut-off frequency is achieved compared to a variant with a slight overlap. At the same time, however, the attenuation of the common mode signal component is improved, i.e. this unwanted signal component is better suppressed. Studies have also shown that the resonance frequency can be set precisely with the help of the second outer shielding film, so that a usable frequency band up to e.g. exactly 20GHz can be achieved.

Appropriately, at least one and preferably both shielding foils are multilayered with a conductive layer and with a non-conductive carrier layer. The two screen foils are designed in particular as so-called Al-PET foils. In principle, the outer film can also be designed as a metal film or as an Al-PET - Al film, that is to say with a carrier layer which is provided on both sides with a conductive layer. With a view to effective electrical contacting, the two shielding foils are arranged with their conductive layers or sides facing one another.

Furthermore, the outer screen film is also wound and in particular in the opposite direction to the inner screen film. Good electrical contacting and bridging of the joints of the inner shielding film are thereby reliably achieved. The pair shield can therefore also be referred to as a double-wound helix pair shield.

The outer shielding film is also wound onto a gap, ie adjacent winding sections are spaced apart from one another in the longitudinal direction. The distance, ie the gap, is in the range from 1 to 10% of the width of the shielding film. This version is used in combination with the inner screen film wrapped with a large overlap (20-40% of the width). The resonance frequency can be precisely adjusted through the special selection of the structure and the winding of the second shielding film. In addition, the advantage of the particularly good common mode damping remains.

Furthermore, at least one drain wire is preferably arranged, which is connected in an electrically conductive manner to at least one, preferably both, shielding foils. Such a drain wire is used, for example, for reliable electrical contacting of the pair shielding on a contact part, for example on a plug. According to a first variant, this drain wire is arranged between the two shielding foils and in particular runs parallel to the individual wires, for example in a gusset area. According to a second variant, the drain wire is contacted on the outside of the outer shielding film. Generally, two double wires are preferably arranged symmetrically to a plane of symmetry of the pair of wires. In the case of the outer two wires, these lie on the connecting axis of the two conductors of the pair of wires.

Furthermore, in a useful further development, a fixing film is additionally wound around the pair shielding for a respective pair of wires. This is, in particular, an adhesive film that is glued to the pair shield. This fixes the shield structure of the pair shield. The fixing film is in particular an insulating film, so that a respective pair of shields is electrically insulated from the outside, in particular, for example, to a common outer shield.

In a preferred embodiment, the data cable generally has a cable core or a cable core which comprises a plurality of electrical line components, at least one and preferably a plurality of the lines being formed by the pair of wires provided with the pair shielding.

The cable core expediently has only such wire pairs. The cable core is still surrounded by a common outer shield. This is particularly multi-layered. Optionally or in combination, it has a braid or screen foils, in particular metallized foils, etc., as components. A cable outer sheath is usually in turn arranged around the outer shield.

Due to the structure described here, the data cable and in particular the pair shielding are also suitable for a particularly efficient contact connection of the pair shielding to a circuit board of a typical plug (small form pluggable SFP +, SFP28, QSFP28 ...) for high-speed data transmission (so-called paddle card ). In the unpublished at the time of registration DE 10 2013 225 794.5 Such a preferred contact connection is described with the title "contact connection of shielded data lines on a circuit board and method for contacting several shielded data lines on a circuit board". In a prefabricated state, the data cable is therefore connected to such a connector.

Exemplary embodiments of the invention are explained in more detail below with reference to the figures.

Figur 1

eine Querschnittdarstellung eines mit einer Paarschirmung versehenen Adernpaares,

Figur 2

eine Seitenansicht des in Figur 1 gezeigten Adernpaares,

Figur 3

eine ausschnittsweise vergrößerte Darstellung der Paarschirmung in einem Überlappbereich,

Figur 4

eine Querschnittsdarstellung eines Datenkabels gemäß einer ersten Ausführugsvariante

Figur 5

eine Querschnittsdarstellung eines Datenkabels gemäß einer zweiten Ausführugsvariante sowie

Figur 6

ein Diagramm, bei dem die Einfügedämpfung I gegenüber der Frequenz in GHz für unterschiedliche Paarschirmung bei einem symmetrischen Adernpaar dargestellt ist.

The figures each show in simplified representations:

Figure 1

2 shows a cross-sectional representation of a pair of wires provided with a pair of shielding,

Figure 2

a side view of the in Figure 1 shown wire pair,

Figure 3

3 shows an enlarged representation of the pair shielding in an overlap area,

Figure 4

a cross-sectional view of a data cable according to a first embodiment

Figure 5

a cross-sectional view of a data cable according to a second embodiment and

Figure 6

a diagram in which the insertion loss I versus frequency in GHz is shown for different pair shielding with a symmetrical pair of wires.

Parts with the same effect are provided with the same reference symbols in the figures.

One for a high-speed data cable 2 (cf. Figures 4,5 ) used pair of wires 4, which is provided with a pair of shielding 6, is in Figure 1 shown. The pair of wires 4 consists of two wires 8, each of which is in turn formed by a central conductor 10, which is encased by insulation 12. The conductor 10 is usually a solid solid conductor. Alternatively, stranded wires can also be used.

The two wires 8 preferably run parallel to one another and are therefore not twisted together.

The pair of wires 4 is surrounded overall by a multi-layer pair shield 6, which has an inner shield foil 14 and an outer shield foil 16. The pair shield 6 is in particular finally formed by these two shield foils 14, 16. The pair shield 6 is finally surrounded, in particular wrapped, by a fixing film 18, which is designed in particular as an adhesive film. The fixing film 18 is made of plastic and is not electrically conductive, that is, electrically insulating.

Supplementary is in Figure 1 an optional drain wire 20 is shown, which is preferably placed in a gusset area of the two wires 8. The The drain wire 20 is also arranged in particular between the two shield foils 14, 16. Alternatively, two double wires 20 are preferably contacted on the outside with the outer shielding film 16, as is shown, for example, in FIG Fig. 5 is shown. The two additional wires 20 lie on an imaginary plane of symmetry or connecting line of the two conductors 10. When the at least one additional wire 20 is placed on the outside, the latter is held in particular between the outer shielding film 16 and the fixing film 18.

The pair of wires 4 together with the pair shield 6 and the fixing film 18 and possibly the two wires 20 is also referred to below as a shielded pair 30.

The two screen foils 14, 16 are each preferably metal-coated plastic foils, in particular so-called AL-PET foils. These each have a carrier layer 22 designed as an insulating layer, on which a conductive layer 24 is applied (cf. in this regard in particular Figure 3 ). In the case of external double wires, the outer side of the outer shielding film 16 must also be designed as a conductive layer 24. The outer shielding foil 16 is then, for example, a carrier layer 22 with conductive layers 24 applied on both sides or a metal foil which basically has conductive layers 24 on both sides.

The two shielding foils 14, 16 are oriented in such a way that their respective conductive layers 24 face one another and, in particular, touch one another, so that the two conductive layers 24 are electrically conductively contacted.

How from Figure 2 the inner shielding film 14 is wound helically around the pair of wires 4. The shielding film 14 is usually wound with a very slight pitch, that is to say very closely. The lower the slope, the more the undesirable resonance effect shifts to higher frequencies. The slope is typically only a few mm, for example in the range of 2 up to 6 mm, ie for each 360 ° wrap the screen film propagates 2 to 6 mm in the longitudinal direction 28.

The inner screen film 14 is wound with an overlap 26, that is to say that winding sections adjoining one another in the longitudinal direction 28 overlap. According to a preferred embodiment, this overlap 26 is approximately one third of the width B of the inner screen film 14.

The outer screen film 16 is preferably also wound, but in the opposite direction to the inner screen film 14. For example, it has the same slope as the inner screen film 14. Alternatively, the slope deviates from this and is, for example, less or also greater. The outer screen film 16 can also have an overlap or be wound in a butt joint.

In a preferred embodiment, however, it is wound on a gap, so that a distance A is formed between two adjacent winding sections. The distance A is, for example, in the range from 1 to 5% of the width B of the outer screen film 16.

The fixing film 18 is in particular a plastic carrier film provided with an adhesive layer. This is preferably also wound (in Figure 2 not shown).

Based on the enlarged, partial representation according to Figure 3 The pair of shield 6 in an overlap area can be seen that the inner screen film 14 in its opposite edge areas, ie in the overlap area 26 with the conductive layer 24 facing outwards. The inner screen film 14 is therefore not folded over in the edge regions. In the overlap region 26, the inner shielding film 14 therefore has an alternating layer sequence between the carrier layer 22 and the conductive layer 24. As a result, the edge regions of the conductive layer 24 of the inner shielding film 14 in the overlap region 26 are separated from one another in an insulating manner, which leads to the resonant circuit described at the outset with the undesired resonance frequency, as a result of which in particular at higher frequencies Frequencies> 5 Ghz unwanted damping occur as a result of the resonance effects. These undesirable effects are at least reduced by the additional measure of the outer screen film 16 described here. At the same time by the in the embodiment Figure 3 selected overlap 26 attenuated the unwanted common mode signal.

Usually, a plurality of lines 30 are combined in a cable core 32 in a data cable 2, as is shown in FIGS Figures 4, 5 is shown. In the two variants, the cables are each shielded pairs 30. In addition, however, other cable types can also be integrated.

The two in the Figures 4, 5 Variants of the data cable 2 shown differ in particular with regard to the structure of the individual shielded pairs 30. In the variant according to Figure 4 shielded pairs 30 are used, as is the case with the Fig. 1 have been described.

In the variant according to the Figure 5 an alternative embodiment is used. In this case, two double wires 20 are arranged on the outside between the outer shielding film 16 and the fixing film 18.

In both variants - as shown in the exemplary embodiment - two shielded pairs 30 are initially wrapped in a plastic film. This core area is then surrounded on the circumference by a plurality of further pairs 30, which are shielded in the exemplary embodiment 6.

This and thus the cable core 32 is preferably surrounded by a multi-layer jacket structure. In such data cables 2, the cable core 32 is generally surrounded by a common outer shield 34. In the exemplary embodiment, an inner layer of plastic film is additionally wrapped around the cable core 32.

In the exemplary embodiment, the outer shield 34 is constructed in multiple layers with a combination of a foil shield 36 and, for example, a braided shield 38. Finally, this outer screen 34 is surrounded by a common cable sheath 40.

In Figure 6 the so-called insertion loss I of different shielded pairs of different types is compared with the frequency of the transmitted data signal (in GHz). Curves A and B show conventional design variants. Curve A represents a shielded pair, which is only wrapped by a single-layer shielding film. In contrast, curve B represents a shielded pair, which is surrounded by a longitudinally folded shielding film.

In addition, curve B also tends to indicate a course such as is obtained in the previously described winding variant with the inner film 14 wound with only a slight overlap 26.

Curve C shows a variant showing a course, such as that with the shortest pitch of the winding of an Al-PET film, e.g. when using a 26AWG wire (American Wire Gauge). With an extremely short winding, the cut-off frequency can therefore be shifted to higher frequencies.

Curve D indicates the course of the curve obtained in the second variant described above, in which the outer shielding film 16 is preferably wound with a small gap A in the range of, for example, about 3% of the width of the shielding film 16, such as this too Figure 2 has been described. At the same time, the inner screen film 14 is preferably wound with a large overlap 26 of, for example, approximately 30% of the width.

As can be clearly seen, the insertion loss for a conventional pair of wires provided with a wound pair shield (curve A) increases sharply from a signal frequency of approximately 5 GHz. Such a data cable is therefore only of limited use for higher signal frequencies.

On the other hand, a pair of wires 4 (curve B) provided with a longitudinally folded shielding film shows a significantly smaller increase in attenuation even in higher frequency ranges of well over 25 GHz even at higher frequencies> 5 GHz. However, as stated at the beginning, this is bought with an undesirable increase in the so-called common mode signal.

By means of the special pair shielding 6 described here, the course of the insertion loss approximates the course which is achieved with longitudinally folded pair shields (curve B). Such a pair of shielding 16, formed from the two shielding foils 14, 16, therefore still shows an acceptable attenuation even at higher frequencies above 10 GHz, so that such a data cable 2 is also suitable for the transmission of high-frequency data signals.

In sum, the special structure of the pair shield 6 described here gives the following advantages: the resonance effect (which forms a type of bandstop) is prevented or at least shifted to significantly higher frequencies. At the same time, the common mode signal is effectively suppressed by the overlap 26. Overall, the disadvantages of a longitudinally folded pair shield are significantly reduced, at the same time the undesirable resonance effect in the case of coiled shields is expanded at least to a non-disturbing frequency range greater than 10 GHz and preferably greater than 15 or 20 GHz. The helical wrapping also simplifies production. In the case of longitudinally folded pair shields, film formation requires greater wear. The overlap point also creates an asymmetry and overall the pairs are less flexible due to the longitudinal film. Furthermore, the longitudinal film has disadvantages for production. Each individual dimension requires its own form unit.

Reference list

2nd

Data cable

4th

Pair of wires

6

Pair shielding

8th

Vein

10th

ladder

12th

insulation

14

inner screen film

16

outer screen film

18th

Fixing film

20th

Double wire

22

Carrier layer

24th

conductive layer

26

overlap

28

Longitudinal direction

30th

management

32

Cable core

34

Outer screen

36

Foil shielding

38

Braided screen

40

Cable sheath

B

width

A

distance

Claims (9)

1. Data cable (2) for high-speed data transmissions having at least one core pair (4) comprised of two cores (8), which are surrounded by a film-like pair shield (6), wherein
   the pair shield (6) is provided with an inner shielding film (14) and an outer shielding film (16) and the two shielding films (14, 16) are in mutual electrical contact, and the inner shielding film (14) is wound around the core pair (4), the outer shielding film (16) is wound around the inner shielding film (14) in a gapped arrangement, characterized in that the gapped arrangement lies within a range from 1 to 10% of the width of the outer shielding film (16) and in that the inner shielding film (14) is wound with an overlap (26) within a range between 20% and 40% of the width (B) of the inner shielding film (14).
2. Data cable (2) according to the preceding claim, characterized in that
   it comprises a plurality of core pairs (4), and each of the core pairs (4) is surrounded by the pair shielding (6) comprised of the two shielding films (14, 16).
3. Data cable (2) according to one of the preceding claims, characterized in that
   the cores (8) are configured in a mutually parallel arrangement.
4. Data cable (2) according to one of the preceding claims, characterized in that
   at least the inner shielding film (14) is configured in a multi-layer arrangement, and comprises a conductive layer (24) and a substrate (22) .
5. Data cable (2) according to one of the preceding claims, characterized in that
   the two shielding films (14, 16) are configured with conductive layers (24) in a mutually facing arrangement.
6. Data cable (2) according to the preceding claim, characterized in that the outer shielding film (16) is wound in the opposite direction to the inner shielding film (14).
7. Data cable (2) according to one of the preceding claims, characterized in that
   one sheath wire (20), which is bonded to at least one of the shielding films (14, 16), is arranged either between the shielding films (14, 16) or on the outer side of the outer shielding film (16).
8. Data cable (2) according to one of the preceding claims, characterized in that
   a fixing film (18) is additionally wound around the pair shielding (6) of each respective core pair (4).
9. Data cable (2) according to one of the preceding claims, characterized in that
   it comprises a cable core (32) with a plurality of conductors (30), wherein at least one, and preferably a plurality of conductors (30) are constituted respectively by a core pair (4) provided with the pair shielding (6), and in that the conductor core (32) is surrounded by an outer shielding (34).

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